174 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



saxifrage [Chrysospleniuin oppositifoHum), Lastrea dilitata and 

 nettle ( Urtica dioica) to develop beneath it, but later in summer, 

 when the shade condition was established, only Lastrea dilitata 

 and nettle ( Urtica dioica) persisted. The shade of the Wych elm 

 {Ulmus Montana) was observed to have a similar effect on the 

 ground-vegetation, though perhaps not quite to such a marked 

 extent. The ground flora forming a carpet over the major 

 portion of this wood consists essentially of lesser celandine, 

 golden saxifrage, wood-sorrel and species of mosses. So that 

 in the development of its ground flora, as of its tree species, the 

 mixed plantation would seem to present the most varied type of 

 all the woodlands and plantations discussed. 



Summarising what maybe termed the " Urwald " associations 

 of the area under consideration, they appear to assort themselves 

 as follows : — 



1. Birch (which has a range extending from the lower to the 

 upper limits of tree-growth, and has the widest distribution of the 

 three types) consists of two more or less distinct associations — 



{a) Birch-oak association ; this has replaced oak 



"Urwald." 

 {b) " Birch-scrub " association ; this occurs typically on the 



upper limits of tree-growth, and extends over large 



areas in the Highlands. 



2. Scots pine (which, either by itself or accompanied by birch, 

 ascends to the upper limits of tree-growth, but only in rare cases 

 descends to such low elevations as oak and birch. Next to birch 

 it has the widest distribution of the three species), and comprises 

 really only a single association — 



{a) Scots pine association ; this occurs on the middle hill 

 slopes, and is essentially Highland. 



3. Oak (which occupies positions along the lower limits of 

 tree-growth, and of the three associations has probably the most 

 limited range) contains at least three distinct associations — 



(a) Oak-association ; which occurs most typically in the 



lowlands, in parks and enclosures. 

 {b) Oak-coppice association ; this has a wide distribution 



along the lower Umits of tree-growth in the Highlands, 



but is not confined to the Highlands. 

 {c) High-forest oak-coppice association : this has a very 



limited distribution. 



